AV1 to M4B Converter

Convert AV1 to M4B: What This Tutorial Covers

M4B is the MPEG-4 audiobook file — the same container as M4A, but the extension tells audiobook apps to remember where you stopped listening and to show chapters when the file has them. This page takes the soundtrack out of an AV1 video and writes it as an M4B, which is what you want for a lecture, a recorded interview, a sermon or a narrated video you would rather listen to than watch. The walk-through below covers the one thing that decides whether the result has sound at all, the bitrate settings that matter for speech, and what M4B genuinely cannot do.

How to Convert AV1 to M4B

1. Upload Your AV1 File: Drag and drop the file onto the page or click "+ Add Files" to browse. Several files can be queued and they all convert with the same settings.
2. Set the Bitrate under File Compression: File Compression opens on the Quality Preset dropdown, the automatic mode — it shows "Highest" on load, but nothing is actually selected there, and it is the least predictable control on the page. Switch it to Constant Bitrate, the setting that maps one-to-one onto the encoder (the dropdown runs from 8 kbps to 384 kbps and opens on 128 kbps), to Custom Bitrate or Specific file size to name an exact figure, or to Variable Bitrate and one of its five AAC bands (96k-112k down to 20k-32k).
3. Adjust Channels, Sample Rate or Trim: Audio Channel folds a stereo source to Mono — worth doing for a single narrator — Audio Sample Rate steps down to 24000, 16000, 12000 or 8000 Hz for speech, and Trim switches from Unchanged to a Start time and Duration so you only export the part you need.
4. Convert and Download: Click Convert and save the .m4b. Files upload over an encrypted connection, convert on our servers, and are deleted automatically after a few hours. No sign-up, no watermark.

Walk-through: Will Your M4B Actually Have Sound?

Almost always, yes — but it is worth understanding why, because .av1 is an unusual extension. AV1 is a codec, not a container: the Alliance for Open Media's AV1 1.0.0 bitstream specification, published in 2018, describes how to code pictures and says nothing about audio. So a filename ending in .av1 is a codec name being used as a file extension, and what is actually inside depends on who wrote it.

• AV1 files produced here are Matroska streams. When our converter writes AV1 output, the video is muxed into a Matroska container along with the original audio track. Feed that file back in and there is a real soundtrack to extract, so the M4B comes out with audio.
• Most .av1 files from other tools are the same story — a container (usually Matroska, sometimes MP4 or IVF) whose video happens to be AV1, saved under a codec-flavoured extension.
• A genuinely raw AV1 elementary stream is the exception. If someone dumped nothing but Open Bitstream Units to disk, that file codes picture only and has no audio track anywhere in it. An M4B made from one of those is silent, and no converter can change that.

If the file you have on disk actually ends in .mp4, .mkv or .webm, use the tool that matches the extension — MP4 to M4B, MKV to M4B or WebM to M4B — rather than renaming it. Detection is based on what is inside the file, but starting from the right page avoids confusion when a batch mixes formats.

Picking a Bitrate for Spoken Word

Sizes below are simple arithmetic from the bitrate, so you can budget before uploading a long recording (MB here means 10^6 bytes).

M4B, M4A or MP3?

Common Errors and How to Fix Them

• "The M4B is silent." Either the source truly is a raw AV1 elementary stream with no audio track, or the video was exported without sound in the first place. Play the original in VLC and check whether it has an audio stream before blaming the conversion.
• "There is no chapter list." A flat recording has no chapter data to carry over, so you get one continuous track inside an audiobook wrapper. Resume position still works; named chapters do not appear from nowhere.
• "My player restarts the file instead of resuming." Resume behaviour comes from the app, not the file. Apple Books, VLC and dedicated audiobook players honour .m4b; a generic music player treats it as a song and starts over.
• "It will not open on my Android phone." Stock Android players often ignore .m4b. Install an audiobook player that supports it, or convert to AV1 to MP3 for a file that plays anywhere.
• "The file is enormous." You are probably at a high bitrate in stereo. Set Audio Channel to Mono and choose a Constant Bitrate of 48 or 64 kbps — the table above shows what that saves across ten hours.

When This Doesn't Work

This tool makes one M4B from one source file with audio controls; it is not an audiobook production suite. It does not stitch several parts into a single book, author named chapter markers, or attach cover art. For a chaptered, multi-part audiobook, produce the audio first and assemble it with a dedicated builder such as Audiobook Binder, Chapter and Verse or the m4b-tool command line. To break a long recording into pieces by time instead, run the audio through the Audio Cutter. And if you wanted the picture kept rather than the sound extracted, convert to a video target such as AV1 to MP4 — M4B discards video by definition.

Frequently Asked Questions

Will my AV1 to M4B conversion actually contain audio?

Yes, as long as the source has an audio track — which nearly all of them do. Despite the codec-flavoured extension, a .av1 file is normally a container carrying AV1 video plus a separate audio stream; the AV1 files our own converter produces are Matroska streams with the soundtrack preserved. The only case that yields a silent M4B is a genuinely raw AV1 elementary bitstream, which codes picture only and has no audio inside it to extract.

Which codec ends up inside the M4B, and can I choose a different one?

AAC, and no — this is the one audio target here with no codec dropdown, because the MPEG-4 audiobook container is defined around AAC and our encoder registry lists AAC as the only valid audio essence for .m4b. That is a feature rather than a limitation: AAC in an MPEG-4 wrapper is exactly what Apple Books and every audiobook app expects. If you want Opus, Vorbis or FLAC instead, convert to AV1 to OGG or AV1 to FLAC and give up the audiobook behaviour.

Does converting to M4B create chapter markers?

No. M4B is the container Apple uses for audiobooks precisely because it can hold chapter markers and a listening position, but those markers have to exist in the source or be authored deliberately. A single flat recording becomes one continuous track inside an audiobook wrapper — apps will still remember where you stopped, but there is no chapter navigation. Building real chapters means splitting the audio into parts and assembling them in a dedicated audiobook tool.

What is the difference between M4B and M4A?

Technically almost nothing: both are MPEG-4 containers holding AAC audio, and a file renamed from one to the other still plays. The difference is entirely in how software reacts to the extension. .m4b signals "this is a book", so audiobook apps track your position, offer variable playback speed and surface chapters; .m4a is filed as a music or podcast track and usually restarts from zero. Choose M4B for anything you listen to in long sittings, and AV1 to M4A for anything that belongs in a music library.

What bitrate should I use for a lecture or narration?

For a single voice, set Audio Channel to Mono and pick a Constant Bitrate between 48 and 64 kbps — that is roughly 22 to 29 MB per hour, so even a ten-hour recording stays under 300 MB. Push to 96 or 128 kbps only when there is music, several speakers in a room, or a stereo field worth keeping. Dropping the Audio Sample Rate to 24000 Hz saves a little more on speech-only material, though it audibly dulls anything musical.

Can I join several video files into one audiobook here?

Not on this page — each queued file converts independently, so five AV1 lectures come back as five separate M4B files with the same settings applied. That is usually what you want for a lecture series, since each file keeps its own resume position. For a single continuous book you would merge the audio afterwards in an audiobook builder, which is also where chapter markers and cover art get added.

Can I play the M4B on Windows, Android or a car stereo?

On Windows, VLC and iTunes both open M4B without complaint. On Android you generally need an audiobook player that recognises the extension, because stock media players tend to skip it. Car stereos and older hardware are the least predictable — many read .m4a but ignore .m4b. If the destination is unknown or elderly, AV1 to MP3 is the safe choice at the cost of losing resume support.

How large a file can I upload, and what happens to it afterwards?

The practical constraint is upload size and time over your own connection rather than a feature cap, and video sources are the slow part — a multi-hour AV1 file takes a while to send even though the M4B that comes back is small. Trimming to a Time Range before converting does not reduce the upload, but it does cut the output. Your file travels over an encrypted (TLS) connection, is processed on our servers, and both the upload and the finished M4B are deleted automatically after a few hours. No sign-up, no watermark, never shared or made public.